1. Field of the Invention
The present invention relates to an image forming apparatus such as a multi-function peripheral having two or more functions of a copier, printer, scanner and facsimile, and in particular an electrophotographic image forming apparatus.
2. Description of Related Art
Generally in the electrophotographic image forming apparatus, an image is formed on a recording material as follows. An electrostatic latent image is formed on an image forming body such as a photoconductor, the formed electrostatic latent image is developed with toner to form a toner image, and the toner image formed on the photoconductor is directly transferred to a recording paper or is transferred to an intermediate transferring body and subsequently is transferred from the intermediate transfer body to the recording paper.
In the image forming process of the electrophotography, various materials are used as the recording material. That is, thin paper, board paper, glossy paper having a gloss layer on a side where an image is formed, OHT and the like are used as the recording material.
These recording materials have different properties which affect the image forming by electrophotography each other, such as conveyance property, resistance, heat capacity and the like. Thus, in developing, transferring and fixing, it is required that the conditions in the image forming are determined according to the recording materials.
For example, it is proposed in JP 2000-172115A (hereinafter referred to as patent document 1) to switch a printing sequence condition in accordance with specifying information to specify the kind of the recording material.
As for the printing sequence condition, developing sleeve circumferential velocity, development bias value, primary transferring bias value, secondary transferring bias value, secondary transferring velocity, fixing velocity and the like are given.
In patent document 1, scattering, fog and hollow of an image caused by the difference in recoding materials are prevented.
Recently, there is increasing application of the image forming apparatus as an output device of a digital camera, and there is increasing use of glossy paper as the recording material. Fog is extremely problematic in using glossy paper and it is required taking some measure for the problem of fog. This is due to the following phenomenon. In glossy paper, since melted toner is not penetrated or poorly penetrated into the recording material, the melted toner is fixed with spreading on the surface of the recording material in fixing process. Therefore, it occurs that a dot of minute area causing the fog is expanded to a dot of large area.
Due to this phenomenon, even if the fog on the photoconductor and the recording material is low, it becomes high level and may exceed permissive level after fixing process.
Above-described problem of fog after fixing process, which occurs in the case of using glossy paper having flat surface and high glossiness, becomes prominent when a high quality image are formed using toner of small particle size, because the toner of small particle size easily causes the fog.
In patent document 1, the fog prevention is controlled in accordance with differences in properties of the recording materials. However, any measure for the above-described phenomenon of fog is not employed, the phenomenon of fog is that low level fog counted for nothing before the fixing process becomes high level fog by the fixing process. Thus, prevention of fog in using glossy paper is not sufficient.